Most if not all of building codes in the United States require that any bedroom located in a basement have a window that permits an occupant egress therethrough so that the person can safely exit the bedroom in the case of fire or other catastrophe. Basements in older homes typically have relatively small windows located near the top of a concrete or block foundation that are not sufficiently large to permit the necessary egress. Accordingly, to place a bedroom in such a basement, the owner must retrofit the structure by installing a larger egress capable window.
Traditionally, the process of removing a smaller window and retrofitting the basement with a larger window is both time-consuming and costly. For instance, to replace a standard 30.5″×20″ window with a similarly wide but much longer (˜47″) egress window, a much wider opening (at least 3″ or more) must be made in the foundation to account for the installation of wooden structural framework around the window to both support the window as well as provide a foundation load transfer path around the window.
When basement windows are installed in a cast concrete, a concrete block or a brick foundation during original construction, a steel window buck is typically cast or grouted in place. This buck acts to transfer the load around the window and maintain load transfer capability in the portion of the foundation wall in which the window resides.
When retrofitting the smaller window with longer one of similar width, the steel load carrying buck is removed effectively reducing or even eliminating the load carrying capacity of the associated portion of the foundation. In a continuous footer type foundation, the localized reduction in load carrying capacity is primarily confined to the particular portion of the foundation wall and depending on the span of opening will not be detrimental to the residential structure if the load carrying capability is restored shortly thereafter. However, concerning pier-type foundations wherein the foundation wall acts as a load carrying web to transfer load laterally between piers, the effect of effectively severing the load transfer when the buck is removed can cause immediate structural problems.
To mitigate any problems that might result from the removal of the steel window buck and because prior art retrofit wood framework does not carry or transfer load around a window very effectively, structural engineers will often require a retrofitter to install a header of steel L-channel to the sill of the foundation wall immediately above the location of the window that spans a sufficient distance on either side of the planned opening. One leg of the L-channel is placed flush against the top surface of the sill while the perpendicular other leg rests against the inside wall of the foundation. The plate is pined, bolted or otherwise secured to the foundation wall. Accordingly, when the opening is subsequently cut, any load that was carried by the wall and the original window's steel buck is transferred to and carried by the L-channel. If the associated interior basement wall is finished, demolition of the finished wall is typically required to install the L-channel greatly increasing the cost of the retrofit.
The L-channel is almost always left in place even after the egress window is installed. This permits the installer to use less stout framing for the window which is easier and less expensive to install. For instance, 2×4 dimensional studs can be used to provide the framework for the window.
There are several problems with posed with using an L-channel header. First, an L-channel header increases the cost and time required to install an egress window. Additionally, in many older basements the top surface of the foundation may be located only a few inches above the top of the window. Where an L-channel having 4″ or longer legs is specified, the vertical leg of the channel may extend over the top of the opening. With a basement window the most and best light is transmitted into the space from the portions of the window proximate the top edge thereof as the light entering the space from the lower portions is usually not direct but reflected off of a window well. Accordingly, even a couple inches of L-channel overhang can significantly block the amount and quality of light entering an associated space. Finally, pinning or fastening the L-channel to the sill can be very difficult since locating the pins too close to the wall's edge (typically less than 4″) can cause cracking and localized failure of the wall in this region. Accordingly, even large and wider L-channel may be required.
In other egress window retrofits where no L-channel is utilized, the framework surrounding the window must be more stoutly configured to carry the attendant loads. The framework is typically comprised of dimensional lumber or steel. In either instance, the cost associated with fabricating the frame on site and securing it to the foundation can be very expensive as well as time consuming. Where a wood frame is utilized the height of a header can necessitate the lowering of the new window's top edge.
Ultimately, using prior art materials and methods, retrofitting a small basement window with an egress capable window to facilitate providing an extra bedroom in a basement is both costly and time consuming adding significantly to the cost of finishing a basement. Further, if the retrofit is not properly done, damage to the foundation and ultimately the above grade structure of a residence can result.